The present invention is directed to a gate driver integrated circuit for driving MOS gated devices and, more particularly, to a gate driver integrated circuit suitable for use in a resonant power supplies or in electronic ballast circuits.
Electronic ballast circuits for driving fluorescent lamps or other gas discharge illumination devices are coming into widespread use because of the availability of power MOSFET switching devices to replace the previously used bipolar transistor devices. Typically, the electronic ballast circuit uses two power MOSFET switches in a totem pole (half bridge) arrangement which includes one or more LC series resonance circuits and in which the lamp or lamps are connected across one of the reactances of the LC circuit. The power MOSFET switches are driven to conduct alternately by inputs from the secondary windings of a current transformer whose primary winding conducts the current of the lamp circuits. The primary winding current alternates at the resonance frequency of the resonant circuit.
Recently, integrated circuit MOS gate driver devices (MGDs) have been introduced in place of the current transformers. These integrated circuit devices drive the power MOSFETs and IGBTs of an inverter circuit in the ballast circuit from logic level ground referenced inputs and provide a self-oscillating function which is particularly suited for use in electronic lamp ballast circuits. The integrated circuit devices significantly save cost, weight and space when compared to driver circuits employing current transformers.
An example of an MGD is the IR2155 device available from International Rectifier Corporation. This device provides a self oscillating function which has been found to be particularly suited for use in inverter circuits such as are used in electronic lamp ballast circuits.
The MGDs typically have alternating high side and low side outputs for driving the two half bridge power MOSFET switches. Internal circuitry is generally included to provide a fixed, predefined dead time between the alternating high side and low side outputs. The IR2155 MGD, for example, provides a nominal 1.2.mu. sec dead time between outputs. The value of the predefined dead time, however, could be fixed depending on the particular application of the MGD to 1) prevent cross-conduction currents from flowing in the half bridge switches, and 2) allow an external "snubber" circuit to control the half bridge output voltage slew rate to reduce radiated EMI noise.
It is desirable, however, to have the capability of varying the dead time of the MGD. By varying the dead time, the width of the output pulses supplied to the half bridge switch can be varied, thereby changing the on-time of the respective switches. As a result, the energy supplied also changes.
Moreover, the resonant frequency of the load of a power supply circuit, such as that of the lamps in a ballast circuit, may also change over time. It is therefore also desirable to be able to change the dead time of the circuit to shift the on-time of the switches to synchronize with this change in dead time. Thus, it is desirable that the dead time be controlled in a feedback arrangement from the load.
It is further desirable that the dead time control circuitry be incorporated into the same monolithic integrated circuit that includes the MGD.